Flow cytometers are used to analyze particles contained in a sample. In a flow cytometer, a sample containing particles is caused to flow through a flow cell where the particles in the sample flowing through the flow cell are irradiated by light from a light source.
In Japanese Laid-Open Patent Application No. 2008-32659, a collimator lens is used to convert the light from the light source into parallel light rays, a cylindrical lens is used to condense the light in a direction perpendicular to the flow in the flow cell, and a condenser lens is used to condense the light on the flow cell.
In Japanese Laid-Open Patent Application No. 2008-32659, a spherical lens is used as the condenser lens. However, large amount of distortion occurs when the rays are condensed by a single spherical lens, such that a condenser lens having a plurality of glued spherical lenses is usually used in order to reduce the distortion. A cylindrical lens also is usually arranged with spacing as a condenser lens. The thickness of the condenser lens, and the spacing of the condenser lens and the cylindrical lens are restricted by the compactness of the flow cytometer.